use std::hash::Hash;
#[cfg(feature = "native")]
use std::str::FromStr;

use borsh::{BorshDeserialize, BorshSerialize};
use ed25519_dalek::{
    Signature as DalekSignature, VerifyingKey as DalekPublicKey, PUBLIC_KEY_LENGTH,
};

use crate::{SigVerificationError, Signature};

#[cfg(feature = "native")]
pub mod private_key {
    use ed25519_dalek::{Signer, SigningKey, KEYPAIR_LENGTH, SECRET_KEY_LENGTH};
    use rand::rngs::OsRng;
    use thiserror::Error;

    use super::{DefaultPublicKey, DefaultSignature};
    use crate::{Address, PrivateKey, PublicKey};

    #[derive(Error, Debug)]
    pub enum DefaultPrivateKeyDeserializationError {
        #[error("Hex deserialization error")]
        FromHexError(#[from] hex::FromHexError),
        #[error("KeyPairError deserialization error")]
        KeyPairError(#[from] ed25519_dalek::SignatureError),
        #[error("Invalid private key length: {actual}, expected {expected_1} or {expected_2}")]
        InvalidPrivateKeyLength {
            expected_1: usize,
            expected_2: usize,
            actual: usize,
        },
    }

    /// A private key for the default signature scheme.
    /// This struct also stores the corresponding public key.
    #[derive(Clone, serde::Serialize, serde::Deserialize)]
    pub struct DefaultPrivateKey {
        key_pair: SigningKey,
    }

    impl DefaultPrivateKey {
        // This is private method and panics if input slice has incorrect length
        fn try_from_keypair(value: &[u8]) -> Result<Self, DefaultPrivateKeyDeserializationError> {
            let value: [u8; KEYPAIR_LENGTH] = value
                .try_into()
                .expect("incorrect usage of `try_from_keypair`, check input length");
            let key_pair = SigningKey::from_keypair_bytes(&value)?;
            Ok(Self { key_pair })
        }

        // This is private method and panics if input slice has incorrect length
        fn try_from_private_key(value: &[u8]) -> Self {
            let value: [u8; SECRET_KEY_LENGTH] = value
                .try_into()
                .expect("incorrect usage of `try_from_private_key`, check input length");
            let key_pair = SigningKey::from_bytes(&value);
            Self { key_pair }
        }
    }

    impl core::fmt::Debug for DefaultPrivateKey {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            f.debug_struct("DefaultPrivateKey")
                .field("public_key", &self.key_pair.verifying_key())
                .field("private_key", &"***REDACTED***")
                .finish()
        }
    }

    impl TryFrom<&[u8]> for DefaultPrivateKey {
        type Error = anyhow::Error;

        fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
            if value.len() == KEYPAIR_LENGTH {
                Self::try_from_keypair(value).map_err(|e| e.into())
            } else if value.len() == SECRET_KEY_LENGTH {
                Ok(Self::try_from_private_key(value))
            } else {
                let err = Err(
                    DefaultPrivateKeyDeserializationError::InvalidPrivateKeyLength {
                        expected_1: SECRET_KEY_LENGTH,
                        expected_2: KEYPAIR_LENGTH,
                        actual: value.len(),
                    },
                );
                err.map_err(|e| e.into())
            }
        }
    }

    impl PrivateKey for DefaultPrivateKey {
        type PublicKey = DefaultPublicKey;

        type Signature = DefaultSignature;

        fn generate() -> Self {
            let mut csprng = OsRng;

            Self {
                key_pair: SigningKey::generate(&mut csprng),
            }
        }

        fn pub_key(&self) -> Self::PublicKey {
            DefaultPublicKey {
                pub_key: self.key_pair.verifying_key(),
            }
        }

        fn sign(&self, msg: &[u8]) -> Self::Signature {
            DefaultSignature {
                msg_sig: self.key_pair.sign(msg),
            }
        }
    }

    impl DefaultPrivateKey {
        pub fn as_hex(&self) -> String {
            hex::encode(self.key_pair.to_bytes())
        }

        pub fn from_hex(hex: &str) -> anyhow::Result<Self> {
            let bytes = hex::decode(hex)?;
            Self::try_from(&bytes[..])
        }

        pub fn default_address(&self) -> Address {
            self.pub_key().to_address::<Address>()
        }
    }

    #[cfg(feature = "arbitrary")]
    impl<'a> arbitrary::Arbitrary<'a> for DefaultPrivateKey {
        fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
            use rand::rngs::StdRng;
            use rand::SeedableRng;

            // it is important to generate the secret deterministically from the arbitrary argument
            // so keys and signatures will be reproducible for a given seed.
            // this unlocks fuzzy replay
            let seed = <[u8; 32]>::arbitrary(u)?;
            let rng = &mut StdRng::from_seed(seed);
            let key_pair = SigningKey::generate(rng);

            Ok(Self { key_pair })
        }
    }

    #[cfg(feature = "arbitrary")]
    impl<'a> arbitrary::Arbitrary<'a> for DefaultPublicKey {
        fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
            DefaultPrivateKey::arbitrary(u).map(|p| p.pub_key())
        }
    }

    #[cfg(feature = "arbitrary")]
    impl<'a> arbitrary::Arbitrary<'a> for DefaultSignature {
        fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
            // the secret/public pair is lost; it is impossible to verify this signature
            // to run a verification, generate the keys+payload individually
            let payload_len = u.arbitrary_len::<u8>()?;
            let payload = u.bytes(payload_len)?;
            DefaultPrivateKey::arbitrary(u).map(|s| s.sign(payload))
        }
    }
}

#[cfg_attr(
    feature = "native",
    derive(serde::Serialize, serde::Deserialize, schemars::JsonSchema)
)]
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct DefaultPublicKey {
    #[cfg_attr(
        feature = "native",
        schemars(with = "&[u8]", length(equal = "ed25519_dalek::PUBLIC_KEY_LENGTH"))
    )]
    pub(crate) pub_key: DalekPublicKey,
}

impl Hash for DefaultPublicKey {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.pub_key.as_bytes().hash(state);
    }
}

impl BorshDeserialize for DefaultPublicKey {
    fn deserialize_reader<R: std::io::Read>(reader: &mut R) -> std::io::Result<Self> {
        let mut buffer = [0; PUBLIC_KEY_LENGTH];
        reader.read_exact(&mut buffer)?;

        let pub_key = DalekPublicKey::from_bytes(&buffer).map_err(map_error)?;

        Ok(Self { pub_key })
    }
}

impl BorshSerialize for DefaultPublicKey {
    fn serialize<W: std::io::Write>(&self, writer: &mut W) -> std::io::Result<()> {
        writer.write_all(self.pub_key.as_bytes())
    }
}

#[cfg_attr(
    feature = "native",
    derive(serde::Serialize, serde::Deserialize, schemars::JsonSchema)
)]
#[derive(PartialEq, Eq, Debug, Clone)]
pub struct DefaultSignature {
    #[cfg_attr(
        feature = "native",
        schemars(with = "&[u8]", length(equal = "ed25519_dalek::Signature::BYTE_SIZE"))
    )]
    pub msg_sig: DalekSignature,
}

impl BorshDeserialize for DefaultSignature {
    fn deserialize_reader<R: std::io::Read>(reader: &mut R) -> std::io::Result<Self> {
        let mut buffer = [0; DalekSignature::BYTE_SIZE];
        reader.read_exact(&mut buffer)?;

        Ok(Self {
            msg_sig: DalekSignature::from_bytes(&buffer),
        })
    }
}

impl BorshSerialize for DefaultSignature {
    fn serialize<W: std::io::Write>(&self, writer: &mut W) -> std::io::Result<()> {
        writer.write_all(&self.msg_sig.to_bytes())
    }
}

impl Signature for DefaultSignature {
    type PublicKey = DefaultPublicKey;

    fn verify(&self, pub_key: &Self::PublicKey, msg: &[u8]) -> Result<(), SigVerificationError> {
        pub_key
            .pub_key
            .verify_strict(msg, &self.msg_sig)
            .map_err(|e| SigVerificationError::BadSignature(e.to_string()))
    }
}

#[cfg(feature = "native")]
fn map_error(e: ed25519_dalek::SignatureError) -> std::io::Error {
    std::io::Error::new(std::io::ErrorKind::Other, e)
}
#[cfg(not(feature = "native"))]
fn map_error(_e: ed25519_dalek::SignatureError) -> std::io::Error {
    std::io::Error::new(std::io::ErrorKind::Other, "Signature error")
}

#[cfg(feature = "native")]
impl FromStr for DefaultPublicKey {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let bytes = hex::decode(s)?;

        let bytes: [u8; PUBLIC_KEY_LENGTH] = bytes
            .try_into()
            .map_err(|_| anyhow::anyhow!("Invalid public key size"))?;

        let pub_key = DalekPublicKey::from_bytes(&bytes)
            .map_err(|_| anyhow::anyhow!("Invalid public key"))?;
        Ok(DefaultPublicKey { pub_key })
    }
}

#[cfg(feature = "native")]
impl FromStr for DefaultSignature {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let bytes = hex::decode(s)?;

        let bytes: ed25519_dalek::ed25519::SignatureBytes = bytes
            .try_into()
            .map_err(|_| anyhow::anyhow!("Invalid signature"))?;

        Ok(DefaultSignature {
            msg_sig: DalekSignature::from_bytes(&bytes),
        })
    }
}

#[test]
#[cfg(feature = "native")]
fn test_privatekey_serde_bincode() {
    use self::private_key::DefaultPrivateKey;
    use crate::PrivateKey;

    let key_pair = DefaultPrivateKey::generate();
    let serialized = bincode::serialize(&key_pair).expect("Serialization to vec is infallible");
    let output = bincode::deserialize::<DefaultPrivateKey>(&serialized)
        .expect("SigningKey is serialized correctly");

    assert_eq!(key_pair.as_hex(), output.as_hex());
}

#[test]
#[cfg(feature = "native")]
fn test_privatekey_serde_json() {
    use self::private_key::DefaultPrivateKey;
    use crate::PrivateKey;

    let key_pair = DefaultPrivateKey::generate();
    let serialized = serde_json::to_vec(&key_pair).expect("Serialization to vec is infallible");
    let output = serde_json::from_slice::<DefaultPrivateKey>(&serialized)
        .expect("Keypair is serialized correctly");

    assert_eq!(key_pair.as_hex(), output.as_hex());
}